Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$6.89	11.869%	$7.7078	$7.71	$7.70	$7.70
Purchase #2	$82.35	4.337%	$85.9215	$85.92	$85.90	$85.90
Purchase #3	$52.88	6.651%	$56.397	$56.40	$56.40	$56.40
Purchase #4	$215.88	4.165%	$224.8714	$224.87	$224.85	$224.90
Purchase #5	$248.30	8.350%	$269.0331	$269.03	$269.05	$269.00
Purchase #6	$35.38	7.522%	$38.0413	$38.04	$38.05	$38.00
Purchase #7	$200.75	10.628%	$222.0857	$222.09	$222.10	$222.10
7 purchase totals =	$842.43		$904.0578	$904.06	$904.05	$904.00